Carbon Isotope Discrimination, Selection Response, and Forage Production of Tall Fescue in Contrasting Environments

Carbon isotope discrimination (Δ) usually correlates with the dry matter to transpiration ratio (transpiration effi ciency) in C 3 species, but its heritability and relationship to forage production are less clear. In a 4-yr study of tall fescue (Festuca arundinacea Schreb.) at Pullman, WA (relatively cool with low humidity), and Ardmore, OK (relatively hot with high humidity). we determined (i) if Δ differences in divergently selected populations made on single plants were maintained in solid seeded plots, and (ii) how Δ in selected populations and a set of four cultivars was related to forage production. Differences in Δ for low and high Δ populations selected on spaced plants were maintained in solid seeded plots at both Pullman and Ardmore. At Pullman, the low Δ selection had higher production than the high Δ selection with the base population intermediate. Partial correlations with all entries between Δ and forage production, controlling for harvest date effects, were not signifi cant. However, partial correlation between Δ and forage production on the selected and base populations was signifi cant (r = −0.59, P < 0.05, n = 12) at Pullman, although not at Ardmore. The data show selection for low Δ may improve forage production in some environments, although not consistently. For breeding tall fescue, one cycle of phenotypic selection for low Δ in advanced material is recommended.